Control circuit for energizing the windings of multi-phase step motors including a two level supply voltage

ABSTRACT

A control circuit for multi-phase step motors includes a driven circuit responsive to timed incoming pulses to excite the motor phases according to a predetermined switching format. A power supply provides energization to the motor windings as the associated phases are excited, the energizing power normally supplied via a substantial dropping impedance. A network is provided in circuit with the dropping impedance to bypass that impedance and supply virtually the total power of the power supply to the windings associated with the excited motor phases, at selectable portions of the switching format.

United States Patent Newell [is] 3,662,245 [451' May 9,1972

[54] CONTROL CIRCUIT FOR ENERGIZING THE WINDINGS OF MULTI-PHASE STEPMOTORS INCLUDING A TWO LEVEL SUPPLY VOLTAGE 21 1 Appl. No.: 885,552

5/ l 969 Newell l 8/696 3,445.74l 5/1969 Gerber... ..3! 8/696 3,452,2636/ l 969 Newell ..3 l 8/l 38 3,486,096 12/ i969 Van Cleave ..3 18/6963,530,347 9/ l 970 Newell ..318/138 Primary Examiner-G. R. SimmonsAnurney- Hurvitz & Rose ABSTRACT A control circuit for multi-phase stepmotors includes a driven circuit responsive to timed incoming pulses toexcite the motor phases according to'a predetermined switching format.

..3l8l6gltiiz3klg/zg2) A power supply provides energizafion to the motorwindings as the associated phases are excited, the energizing power nor-[58] Field of Search ..3l8/l38,254,696, many supplied via a substantialdropping impedance A eh work is provided in circuit with the droppingimpedance to bypass that impedance and supply virtually the total powerof [56] Reknnm Cited the power supply to the windings associated withthe excited UMTED STATES PATENTS motor phases, at selectable portions ofthe switching format. 3,402,334 9/1969 Newton ..318/696 12 Claims, 1Drawing Figure gas 22 srePMnTmz 2kg; i; w A B 4; 0 23 4.9 arm votrneemcaease l8 9 43 7 .Wrmemmsti DRIVER H 52 CONTROL CIRCUIT FOR ENERGIZINGTIIE WINDINGS OF MULTI-PIIASE STEP MOTORS INCLUDING A TWO LEVEL SUPPLYVOLTAGE BACKGROUND OF THE INVENTION The present invention is in thefield of motor control circuits, and is particularly directed to controlcircuits for multiphase step motors by which the normal energization ofthe windings is supplemented at selected phase switchings.

In my U. S. Pat. No. 3,444,447, entitled Multi-Phase Step Motor ControlCircuits Including Means for Supplementing the Normal Energization ofthe windings", l disclose multiphase driver circuitry in which pluralswitching circuits associated with respective phases (e.g., fieldwindings) of a step motor are energized or activated according to apredetermined switching logic program so that each phase is on for acertain period, 'i.e., a time interval during which the correspondingfield winding is excited, and is off for a certain period, i.e., a timeinterval during which the corresponding field winding is unexcited. Eachswitching circuit is constructed and arranged tostore energy from thepower supply for the overall network during the period its associatedphase 1 is off and to supply the stored energy along with the normallyavailable energy from the power supply when the associated phase isturnedon", to compensate for the otherwise relatively slow increase incurrent (and voltage) level in the excited winding(s). This isespecially advantageous when the step motor is operated at highswitching speeds, because the driver provides a torque boost byenhancing the build-up of the torque-producing magnetic field as eachwinding is excited, and without need to vary the level of the powersupply according to the speed at which the motor is operated. In effect,the driver circuit automatically adjusts motor driving torque throughoutany variations in switching sped that may be required during motoroperation.

lnia somewhat different control circuit disclosed in my aforementionedpatent, torque is maintained at a higher than normal level by takingadvantage of the generation of a high voltage reverse polarity spike ona motor winding undergoing transition from the excited state to theunexcited state. According to the latter circuit embodiment, at themoment this reverse voltage surge exceeds a predetermined voltage level,and for the duration of time the surge exceeds that predetermined level,the entire supply voltage, rather than the normal fraction of the supplyvoltage which would otherwise be available, is applied directly acrossthe next winding or windings switched on in the energization format.

SUMMARY OF THE INVENTION The present invention is a variation of thetorque boosting control circuit briefly discussed immediately above, inwhich the application of a supplemental voltage level to a phase(winding) as it is turned "on is independent of any reverse voltagesurge in a winding, and is selectively variable with respect to timing.

Briefly, according to the present invention there is provided a drivercircuit for exciting the windings of a multi-phase step motor in apreselected switching format in which each winding is excited duringcertain preselected time increments and is devoid of excitation duringcertain other preselected increments of the switching formal. A powersupply is connected in energizing circuit relation with the motorwindings and the driver circuit, so that when the windings are excitedby the driver circuit excitation current (voltage) is supplied via thepower supply. An impedance is connected in the energizing circuit tonormally reduce the power excitation level applied to the windings, anda bypass circuit is further connected in the energizing circuit topermit bypassing the impedance to supply substantially the entire powersupply level to the excited winding(s). Means are provided for responseto driver activation pulses to selectively energize the bypass circuitat desired points in the switching format.

The sole FIGURE of drawing is a circuit diagram of a preferredembodiment of the control circuit for energizing the windings of themulti-phase step motor.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the accompanyingdrawing, a step motor 10 is depicted as having four phases A, B, C, Dassociated with windings ll, l2, l3, 14, although a step motor having agreater number of phases might also take advantage of the principles ofthe present invention. Step motor 10 is driven by a conventional drivercircuit 16 which responds to pulses applied to an input path 17 toexcite one or more windings of the motor during intervals when one ormore other windings are de-energized, according to a preselectedswitching format.

The input pulses 18 are to be applied to an input terminal 19 of theoverall control circuit and thence in parallel to path 17 (and driver16) and to an input path 20 of a flip-flop circuit 22. Flip-flop 22 hasa pair of stable operating states, one of which is its normal quiescentstate that is assumed by the flipflop when a trigger pulse is applied tothe reset input terminal or path 23 of the flip-flop..ln the quiescentstate, the voltage level appearing at output terminal 25 is low (forexample, a near zero voltage level) while the voltage level at outputterminal 26 is high (e.g., a positive polarity). Under these conditions,PNP transistor 28 is in a cutoff state (non-conducting), and hence a lowvoltage level or zero voltage appears across'the base-emitter junctionof NPN transistor 29 connected to the common lead 30 of motor 10 viaresistance 31, so that the latter transistor is also in the cutoffstate. The voltage existing at the common lead 30 of motor 10 istherefore the voltage at power supply terminal 33 less the voltage dropacross dropping resistor or current limiting resistor 35 (assuming thatone or more motor windings is connected to a point of referencepotential, e.g., ground, via driver 16).

In the other state of flip-flop 22, assumed by the flip-flop when atrigger pulse is applied to set input terminal 20, output terminal 25 isswitched to the high" level and output terminal 26 is switched to thelow level. Under those conditions, transistor 28 is switched toconduction, thereby raising the voltage level at the base electrode oftransistor 29 to virtually the positive level at terminal 33, and thelatter transistor accordingly also switches to the conductive condition.The voltage level existing at common lead 30 of the motor windings isthen almost the entire positive level at power supply terminal 33 Sinceterminal 25 of flip-flop 22 is at the high" level, capacitor 38 issubjected to charging current via variable resistance 39. It isapparent,then, that the time constant of the charging circuit for capacitor 38may be selected according to the voltage level at the high terminal ofthe flip-flop, the capacitance value of capacitor 38, and the resistancevalue of resistance 39. Since resistance 39 is variable, its value maybe selectively adjusted to set the time constant of the charging networkat any desired value. Depending upon the selected time constant,capacitor 38 will eventually be charged to a level equal to the peakpoint or firing voltage level of unijunction transistor 40, so long asthe high" voltage level continues to appear at flip-flop output terminal25. At that point, the unijunction transistor (UJT) becomes highlyconductive and a positive voltage appears at the normally grounded baseelectrode of that transistor, and thus at the base electrode of NPNtransistor 42. The latter transistor is turned on, causing its collectorto fall suddenly negative, triggering flip-flop 22 to the resetcondition via reset input terminal 23.

In operation of the control circuit of the accompanying drawing, a trainof pulses 18 is applied to network input terminal l9, and in parallel toset input terminal 20 of flip-flop 22 and to input path 17 of drivercircuit 16. The driver thereby turns off" one phase and turns on anotherphase, according to the sequential switching logic format that has beenselected for driver operation. Simultaneously therewith, flipfiop 22 istriggered by the input pulse at terminal 20 from the quiescent or resetstate to the set state, thereby switching transistors 28 and 29 tostates of conduction and applying the full voltage level of the powersupply at terminal 33 to the now energized winding(s) of the step motor.

Provided that the time constant of the charging circuit of capacitor 38has been properly selected, the capacitor is rapidly charged to thefiring level of UJT 40 and as the UJT is rendered conductive it alsoturns on transistor 42 to applying a reset trigger pulse to inputterminal 23 of flip-flop 22. Accordingly, the flip-flop again assumesthe quiescent state and the voltage across the excited motor windings(s)reverts to a level diminished by the voltage drop across limitingresistance 35.

For operation in which these events recur with each input pulse atterminal 19, representative. voltage waveforms are shown at variouspoints in the circuit. The turn-on pulse 48 at output terminal 26 offlip-flop 22 and which is applied to the base electrode of transistor28, is initiated by an input pulse 18 and in turn initiates the highvoltage pulse 50 at the motor common. When the fiip-fiop is reset, attime t, the pulse 48 terminates and in turn causes cessation of voltagesupplement-- ing pulse 50. The effect on the current level in theexcited motor winding is shown in waveform 52. From time to time t thecurrent level in the winding builds up very rapidly to the desiredoperating level, in comparison to the normal rate of build-up (showndotted in waveform 52).

This control circuit causes the current in the windings of the stepmotor to remain at relatively high level at high speed operation, bymomentarily raising the voltage level across the excited motorwinding(s) each time a phase switching occurs. The width of the highvoltage pulse (50) is finite, and as the stepping rate is increased thetime between the high voltage pulses is decreased. Hence, the averagevoltage level across the motor windings increases with increasingfrequency, and tends to enhance the total current, and thus the torque.

It is not essential that the time constant of the charging circuit ofcapacitor 38 be set at a value which will result in repetition of thedescribed operation with each incoming pulse. Instead, the time constantmay be selected to result in charging of the capacitor to the peak pointof UJT40 after a series of input pulses has been applied to terminal 19.At the conclusion of a preselected number of the input pulses (i.e., ablock" of input pulses) thecapacitor is charged to the peak point of theUJT, and the flip-flop reverts to the reset state. This is quitesuitable for operation at a single high stepping rate, in which eventthe power supply level is appropriately selected to provide the propercurrent to the windings.

We claim:

1. A control circuit for exciting the windings of a multiphase stepmotor, said control circuit comprising a driver circuit for excitingsaid windings in a preselected switching format, so that each winding isexcited during certain increments of said format and is de-energizedduring certain other increments of said format, a power supply, meanscoupling said power supply in circuit with said windings and with saiddriver circuit to supply a voltage to said windings upon excitation ofsaid windings by said driver circuit in said preselected switchingformat, said means coupling including a common impedance means connectedbetween said power supply means and all said windings for dropping thevoltage which exists across the excited windings while said impedancemeans is in circuit, and further including switch means connected acrosssaid impedance means and effective when closed to bypass said impedancemeans so as to apply substantially the entire voltage of said powersupply to said windings, and means concurrent with the pulses activatingsaid driver circuit for applying square waves to transfer said switchmeans to its bypassing condition, and RC timing means for timing thedurations of said square waves.

2. Control circuitry for exciting the field windings of a multiphasestep motor, comprising a driver circuit for applying energizing currentpulses to said field windings in a predetermined sequential switchingformat in response to sequential input pulses, means responsive to eachof said input pulses operative concurrently with the initiation of eachof said input pulses for adding a square shaped enhancing pulse ofenergizing current to the then energized one of said field windings, anda common RC timing circuit for completely terminating each of saidenhancing pulses at a predetermined time following initiation of each ofsaid enhancing pulses.

3. The combination according to claim 2, wherein is provided a bistabledevice normally in one state, means responsive to said bistable devicein said one state for blocking said enhancing pulse and in another statefor passing said enhancing state, means responsive to initiation of eachinput pulse for transferring said bistable device to said another state,and timing means responsive to attainment of said another state fortransferring said bistable device to said one state following apredetermined time interval.

4. Control circuitry for a multiphase step motor, said step motorincluding plural field windings, a voltage supply, a voltage droppingresistance, a sequencing driver means for connecting said plural fieldwindings sequentially to said voltage supply via said voltage droppingresistance, a source of repetitive pulses applied to control saidsequencing driver, said sequencing driver being operative in response toeach of said repetitive pulses for transferring energization of saidfield windings by said voltage supply from one to another of said fieldwindings, a normally open switch connected across said voltage droppingresistance, and bistable means responsive solely to said repetitivepulses for transferring the state of said bistable device and forthereby closing said switch.

5. The combination according to claim 4, wherein is provided a timingcircuit responsive to said repetitive pulses for resetting said bistabledevice and thereby opening said switch aftera predetermined timeinterval from said closing.

' 6 The combination according to claim 4, wherein said last meansincludes a bistable device having first and second output terminals,said first output terminal being normally at one voltage and said secondterminal being nornially at another voltage for one stable condition ofsaid bistable device, means connecting said second terminal in controlrelation to said switch, means responsive to each of said repetitivepulses tending to transfer the state of said bistable device and therebychange said another voltage to said onevoltage and said one voltage tosaid another voltage and thereby close said switch, a timing circuitresponsive to said repetitive pulses for resetting the state of saidbistable device after a predetermined time interval from its transferand thereby open said switch.

7. Control circuitry for exciting the field windings of a multiphasestep motor, comprising a plurality of field windings of said step motor,a sequencing driver in cascade with said field windings, said sequencingdriver being responsive to each of control pulses to effect eachsequencing of said field windings, a power supply, a voltage droppingimpedance connected in series with said field windings and saidsequencing driver and said power supply, a switch connected across saidvoltage dropping impedance, a bistable device normally in one state andhaving connections to said switch for maintaining said switchnon-conductive when said bistable device is in said one state and whenin a second state rendering said switch conductive, means responsive toeach of said control pulses tending to drive said bistable device intosaid second state, and timing means responsive to each transfer of stateof said bistable device from said one to said another state forresetting said bistable device after a predetermined time interval.

8. In a step motor system, a step motor having plural stepping windings,a sequencer, a power supply, a source of spaced unidirectional controlpulses, a voltage dropping resistance, means responsive to each of saidcontrol pulses for advancing said sequencer in accordance with asequencing format to pass current from said power supply via saidvoltage dropping resistance to a different one of said steppingwindings, an electronic switch connected across said voltage droppingresistance, a flip-flop connected to said electronic switch so as tomaintain said electronic switch conductive in one state of saidflip-flop and non-conductive in the-alternate state, means responsive toeach of said control pulses for driving said flip-flop into said one ofsaid states, an integrator responsive to said flip-flop when in saidalternative one of said states, and means responsive to said integratorwhen said integrator has achieved a predetermined integration level forresetting said flip-flop to said alternative state.

9. The combination according to claim 8, wherein said integrator is aseries RC circuit having a predetermined time

1. A control circuit for exciting the windings of a multi-phase stepmotor, said control circuit comprising a driver circuit for excitingsaid windings in a preselected switching format, so that each winding isexcited during certain increments of said format and is de-energizedduring certain other increments of said format, a power supply, meanscoupling said power supply in circuit with said windings and with saiddriver circuit to supply a voltage to said windings upon excitation ofsaid windings by said driver circuit in said preselected switchingformat, said means coupling including a common impedance means connectedbetween said power supply means and all said windings for dropping thevoltage which exists across the excited windings while said impedancemeans is in circuit, and further including switch means connected acrosssaid impedance means and effective when closed to bypass said impedancemeans so as to apply substantially the entire voltage of said powersupply to said windings, and means concurrent with the pulses activatingsaid driver circuit for applying square waves to transfer said switchmeans to its bypassing condition, and RC timing means for timing thedurations of said square waves.
 2. Control circuitry for exciting thefield windings of a multiphase step motor, comprising a driver circuitfor applying energizing current pulses to said field windings in apredetermined sequential switching format in response to sequentialinput pulses, means responsive to each of said input pulses operativeconcurrently with the initiation of each of said input pulses for addinga square shaped enhancing pulse of energizing current to the thenenergized one of said field windings, and a common RC timing circuit forcompletely terminating each of said enhancing pulses at a predeterminedtime following initiation of each of said enhancing pulses.
 3. Thecombination according to claim 2, wherein is provided a bistable devicenormally in one state, means responsive to said bistable device in saidone state for blocking said enhancing pulse and in another state forpassing said enhancing state, means responsive to initiation of eachinput pulse for transferring said bistable device to said another state,and timing means responsive to attainment of said another state fortransferring said bistable device to said one state following apredetermined time interval.
 4. Control circuitry for a multiphase stepmotor, said step motor including plural field windings, a voltagesupply, a voltage dropping resistance, a sequencing driver means forconnecting said plural field windings sequentially to said voltagesupply via said voltage dropping resistance, a source of repetitivepulses applied to control said sequencing driver, said sequencing driverbeing operative in response to each of said repetitive pulses fortransferring energization of said field windings by said voltage supplyfrom one to another of said field windings, a normally open switchconnected across said voltage dropping resistance, and bistable meansresponsive solely to said repetitive pulses for transferring the stateof said bistable device and for thereby closing said switch.
 5. Thecombination according to claim 4, wherein is provided a timing circuitresponsive to said repetitive pulses for resetting said bistable deviceand thereby opening said switch after a predetermined time interval fromsaid closing.
 6. The combination according to claim 4, wherein said lastmeans iNcludes a bistable device having first and second outputterminals, said first output terminal being normally at one voltage andsaid second terminal being normally at another voltage for one stablecondition of said bistable device, means connecting said second terminalin control relation to said switch, means responsive to each of saidrepetitive pulses tending to transfer the state of said bistable deviceand thereby change said another voltage to said one voltage and said onevoltage to said another voltage and thereby close said switch, a timingcircuit responsive to said repetitive pulses for resetting the state ofsaid bistable device after a predetermined time interval from itstransfer and thereby open said switch.
 7. Control circuitry for excitingthe field windings of a multiphase step motor, comprising a plurality offield windings of said step motor, a sequencing driver in cascade withsaid field windings, said sequencing driver being responsive to each ofcontrol pulses to effect each sequencing of said field windings, a powersupply, a voltage dropping impedance connected in series with said fieldwindings and said sequencing driver and said power supply, a switchconnected across said voltage dropping impedance, a bistable devicenormally in one state and having connections to said switch formaintaining said switch non-conductive when said bistable device is insaid one state and when in a second state rendering said switchconductive, means responsive to each of said control pulses tending todrive said bistable device into said second state, and timing meansresponsive to each transfer of state of said bistable device from saidone to said another state for resetting said bistable device after apredetermined time interval.
 8. In a step motor system, a step motorhaving plural stepping windings, a sequencer, a power supply, a sourceof spaced unidirectional control pulses, a voltage dropping resistance,means responsive to each of said control pulses for advancing saidsequencer in accordance with a sequencing format to pass current fromsaid power supply via said voltage dropping resistance to a differentone of said stepping windings, an electronic switch connected acrosssaid voltage dropping resistance, a flip-flop connected to saidelectronic switch so as to maintain said electronic switch conductive inone state of said flip-flop and non-conductive in the alternate state,means responsive to each of said control pulses for driving saidflip-flop into said one of said states, an integrator responsive to saidflip-flop when in said alternative one of said states, and meansresponsive to said integrator when said integrator has achieved apredetermined integration level for resetting said flip-flop to saidalternative state.
 9. The combination according to claim 8, wherein saidintegrator is a series RC circuit having a predetermined time constant.10. The combination according to claim 9, wherein said time constant issuch that said predetermined integration level is achieved in the timebetween an adjacent pair of said control pulses.
 11. The combinationaccording to claim 9, wherein said time constant is such that saidpredetermined level is achieved in the time longer than the time betweenan adjacent pair of said control pulses.
 12. The combination accordingto claim 9, wherein said series RC circuit includes a variable timingresistance.